A known valve case housing a spool for an oil control valve is disclosed in JP2009-293555A (i.e., hereinafter referred to as Patent reference 1). When the valve case is formed at an outer shell portion of a resin-made cylinder head cover by an insert molding, a clearance may be generated at contact surfaces of the valve case and the outer shell portion when the resin shrinks. In order to overcome this drawback, the valve case described in Patent reference 1 includes a flange portion having plural penetration holes. According to the disclosure of Patent reference 1, the foregoing construction maintains a close contact state of the valve case and the outer shell portion because the resin provided at an upper side of the flange portion and the resin provided at a lower side of the flange portion retains the flange portion in response to shrinkage of the resin filled in the penetration holes.
A main portion of the valve case disclosed in Patent reference 1 is formed by forming oil passages on a cylindrical housing portion which houses the spool. Thus, according to the construction disclosed in Patent reference 1, when an injection pressure of resin for covering the cylindrical housing portion and/or a pressure generated when the resin shrinks, or the like, is applied in a radially inward direction, the housing portion may be deformed because there is no structure which resists the applied pressure. In order to prevent the foregoing deformation, a pressure-resisting performance may be increased by increasing a thickness of the housing portion. However, this counter measurement is inconsistent with a structure that the cylinder head cover is made of resin in order to reduce the weight.
Drawbacks of the known valve case disclosed in Patent reference 1 will be explained with reference to FIGS. 7A and 7B. FIG. 7A shows a cross-sectional view after a known valve case 106 is formed at a resin-made cylinder head cover 3 by an insert molding. FIG. 7B shows a cross-sectional view during the insert molding. In FIG. 7B, for an explanatory purpose, dies other than a core 132 are not shown.
In order to fix the valve case 106 to the cylinder head cover 3, fixing portions 3a, 3b made of resin are formed on both ends of a housing portion 111 having a cylindrical space 121. In those circumstances, the fixing portions 3a, 3b need to have an inner diameter equal to or greater than a diameter of the cylindrical space 121 so that the fixing portions 3a, 3b do not interfere with a movement of a spool positioned within the cylindrical space 121. Further, a drain space 122 to which oil is discharged needs to be formed at a fore-end side (i.e., right-hand side in FIG. 7A) of the housing portion 111.
In order to achieve the foregoing requirements, generally, an insert molding is performed using a cylindrical slide pin 131 and the core 132 as shown in FIG. 7B. That is, the fixing portions 3a, 3b whose inner diameter is the same with the diameter of the cylindrical space 121 is formed by inserting the cylindrical slide pin 131 having a diameter the same size with the diameter of the cylindrical space 121 for positioning the valve case 106. Further, by arranging the core 132 having a convex shape, the drain space 122 which is in communication with the cylindrical space 121 is formed.
According to the foregoing molding method, in order to form the fixing portion 3a at a fore-end portion of the slide pin 131, the slide pin 131 is required to be formed in a straight shape having a diameter the same size with an inner diameter of the housing portion 111 from a rear end to the fore-end. However, in a case where a diameter of the fore-end of the slide pin 131 is the same size with the diameter of the cylindrical space 121 (i.e., to be precise, the diameter of the slide pin 131 is slightly smaller than the diameter of the cylindrical space 121), the fore-end of the slide pin 131 may readily contact an end surface of the housing portion 111 when inserting the slide pin 131 into the cylindrical space 121. In consequence, the valve case 106 may be flawed or deformed, and/or the slide pin 131 may not be inserted into the cylindrical space 121, which may possibly stop a production line for the molding.
A need thus exists for a valve case for an oil control valve which is not susceptible to the drawback mentioned above.